Counterbalanced two speaker rotary tremolo device

ABSTRACT

A rotary tremolo device employs a pair of outwardly facing speakers mounted in counterbalanced relationship on a rotatable support. The speakers are respectively driven by signals derived from the same source but differing in phase, preferably by 90 electrical degrees, so as to provide an asymmetrical sound radiation pattern. As the support is rotated at about five to eight revolutions per second, a tremolo and vibrato effect is produced. The support may also be rotated at slower or faster speeds to produce other effects.

United States Patent [1 1 Sharp 1 COUNTERBALANCED TWO SPEAKER ROTARYTREMOLO DEVICE [75] Inventor: Paul R. Sharp, Sierra Madre, Calif. [73]Assignee: Columbia Broadcasting System, Inc.,

New York, NY.

[22] Filed: May 26, 1971 [21] Appl. No.: 147,023

[52] US. Cl. 179/1 J, 84/125 [51] Int. Cl. Golh l/OZ [58] Field ofSearch 179/1 .1, 1 D, 1 E, 179/1 GA, 1GY;84/1.25; 181/31 B [5 6]References Cited UNITED STATES PATENTS 2,995,054 8/1961 Leslie 179/1 .13,160,695 12/1964 Bonham... 84/].25 2,869,667 1/1959 Leslie 84/125 Dec.25, 1973 Leslie.... Hare Primary Examiner-William C. Cooper AssistantExaminer-Jon Bradford Leaheey Attorney-Flam & Flam 5 7] ABSTRACT 14Claims, 5 Drawing Figures 22 i DIFFERENQE NETWORK PATENTED UECZS W5SHEET 2 BF 2 COUNTERBALANCED TWO SPEAKER ROTARY TREMOLO DEVICEBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to acoustic pulsato apparatus in which a soundradiation pattern is rotated. In general there are two types of suchapparatus, one in which the acoustic driver is stationary and one inwhich the acoustic driver is rotated. In both cases a rotary soundchannel is provided that cooperates with the acoustic driver. Theacoustic driver is stationary. The rotary sound channel has a mouth thatcontinually registers with the driver at the axis of rotation, therebeing a sound emanating opening which describes an orbital path. In theother type of such apparatus the sound channel is formed by a speakercone at the center of which the acoustic driver is located. If desired,the sound channel may be extended by components cooperating with thespeaker cone. This invention is concerned particularly with the problemof increasing the acoustic power handling capabilities of such deviceswithout increasing the physical size thereof.

2. Description of the Prior Art In order to increase the acoustic powerhandling characteristics of rotary pulsato apparatus, it has beenproposed to provide a pair of sound channels facing radially outward ondiametrically opposite sides of the axis of rotation. A single drum, forexample, may mount two speakers. The arrangement is not satisfactorybecause the sound radiation pattern now repeats twice every revolutionrather than only once every revolution. Since characteristic tremolo andvibrato is produced by a recurrence rate of about five to eightrevolutions per second, the speed of the two-speaker drum must behalved; otherwise, an effect quite different from characteristic tremoloand vibrato will be produced. If the speed is halved, then the orbitalvelocity of the speaker openings is correspondingly halved. The Dopplereffect is accordingly reduced and the frequency or pitch change islikewise reduced. Inorder to restore deep, rich frequency shiftcharacteristic of vibrato, the orbit must be doubled. The result, ofcourse, is an undesired increase in physical size of the rotaryapparatus. In U.S. Pat. No. 3,100,024 to Leslie, a plurality in speakersare mounted upon a common drum in such manner that the combined soundradiation pattern is asymmetrical. Accordingly, the 5 to 8 revolutionsper second rate of the drum can be'maintained while yet producingcharacteristic tremolo and vibrato. In order to accomplish that resulthowever, the Leslie patent required the use of three or more speakers,together with a careful selection of the polarity of drive signals forthe speakers. The structure shown in the Leslie patent is not-operableif two, and only two, speakers are used, unless the speakers themselvesare asymmetrically mounted. But such an arrangement is undesirablebecause counter-weights are required. The

most advantageous arrangement is one in which the speakers are equallyangularly located so that no counter-weight is required. Twodiametrically located speakers cannot create an asymmetrical soundradiation pattern, irrespective of the polarity of drive signals appliedto the respective speakers, for the reason that the resulting pattern iseither a figure eight, the major axis of which is aligned with thespeakers, or a figure eight with the major axis perpendicular to theaxis of the speakers. In both cases, the sound radiation pattern repeatstwice per revolution. The primary object of this invention is to make itpossible to provide two sound channels in diametrically opposedrelationship, in which an asymmetrical sound radiation pattern isproduced notwithstanding the fact that the same source causes the soundchannels to be acoustically driven.

SUMMARY OF THE INVENTION In accordance with one form of the presentinvention, a pair of speakers are mounted in diametrically opposedrelationship on a rotary support. The speakers are driven by a pair ofsignals differing in phase, optimally by electrical degrees, so as toproduce a sound radiation pattern which occurs only once for eachrevolution of the support. By rotating the support at from about five toeight revolutions per second, a full, rich tremolo or vibrato effect isproduced. The speaker drive signals are derived from a single source,e.g., the output of an electronic organ, by using a phase differencenetwork.

The device has the advantage of producing greater acoustic output thancould be provided with a single speaker, while permitting the twospeakers to be mounted in counterbalanced relationship on the rotatablesupport.

In an alternative embodiment, a pair of speakers are mounted in spaced,facing relationship and driven by the appropriately phased signals. Arotary reflector plate or baffle is disposed at an angle to the commonaxis of the speakers. Opposite faces of the baffle reflect the speakersounds in diametrically opposite directions. The sound radiation patternyet repeats only once per revolution due to the quadrature phasing ofthe speaker signals.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of theinvention will be made with reference to the accompanying drawings.

FIG. 1 is an elevational view of a rotary tremolo device in accordancewith the present invention, portions of the rotary support and speakerhousing being shown in section.

FIG. 2 is an electrical schematic diagram of a phase difference networkuseful in conjunction with the device of FIG. 1.

FIG. 3 is a block diagram of another electrical arrangement for drivingthe speakers used in the invention.

FIG. 4 is a simplified elevational view of a two speaker tremolo deviceusing a rotating reflector plate.

FIG. 5 is a graph showing a typical sound radiation pattern from theinventive two-speaker rotary tremolo device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detaileddescription is of the best presently contemplated modes of carrying outthe invention. This description is not to be taken in a limiting sense,but is made merely for the purpose of illustrating the generalprinciples of the invention since the scope of the invention best isdefined by the appended claims.

Structural and operational characteristics attributed to forms of theinvention first described also shall be attributed to forms laterdescribed unless such characaccordance with the present invention. Thedevice 11 includes a rotatable support comprising, in this instance, ahousing 12 having a cylindrical wall 12a and ends 12b, 12c coaxiallysupported on a shaft 13 by means of flanged collars l4, 15. A pair ofspeakers 16, 17 are mounted in diametrically opposed relationship withinthe housing 12. No counter-weight is necessary, since the speaker 16counterbalances the speaker 17.

The cones or sound channels of the speakers 16, 17 face radiallyoutwardly through a respective pair of openings 18, 19 in the housingwall 12a. The speakers 16, 17 are driven with a pair of signalsappropriately differing in phase, optimally by 90 electrical degrees, soas to produce an asymmetrical sound radiation pattern which repeats onlyonce for each revolution of the speaker housing 12. The cabinetstructure is either open or louvered to permit passage of sound producedby the speakers 16, 17.

In the embodiment of FIG. 1, the speaker drive signals are derived bymeans of a phase difference network 21 mounted within the housing 12adjacent the shaft 13. The input to network 21 is a single sourcesignal, typically the output of an electronic organ, supplied via a line22 and amplified by a power amplifier 23. For convenience, the output ofthe amplifier 23 is communicated to the network 21 via a pair ofconductors 24a, 24b, a slip ring assembly 25, and additional conductorsinterior of shaft 13. The slip ring assembly advantageously may be ofthe type described in the US. Pat. No. 3,014,192 to Leslie.

Rotational motion at the five to eight revolutions per second rateappropriate for production of tremolo is imparted to the speaker housing12 by means of a motor 26 connected by a belt 27 and a pulley 28 to theshaft 13. The shaft 13 itself is mounted for rotation between a pair ofball bearings 29, 30 accommodatedby interior partition walls 31, 32forming part of the cabinet structure 10.

The phase difference network 21 may comprise any type of conventionalcircuitry accepts accpets a 'single source signal and provides a pair ofoutput signals of mutually different phase, but corresponding inamplitude and frequency to the source signal. By way of example only,FIG. 2 shows a pair of conventional lattice filters 21a, 21b which maybe employed advantageously to form the phase difference network 21. Thestop band of each lattice filter 21a, 21b is selected to be above thehighest frequency of the amplified source signal supplied via lines 24a,24b, so that each speakers 16, 17 receives via the respective pair oflines 35, 36 a drive signal substantially duplicating the source signal.However, each lattice filter 21a, 21b is designed, in a manner wellknown to those skilled in the filter network art, to provide a phaseshift which is linear with frequency. Moreover, the filter 21a isdesigned to introduce a phase shift which is greater or less than thatintroduced by the filter 21b. Accordingly, the speaker signal on thelines 35 will differ in phase by a constant phase angle from the otherspeaker drive signal on the lines 36. I

Optimally, the drive signals to the speakers 16, 17 should differ inphase by 90 electrical degrees, as this results; in a completelyasymmetrical sound radiation patterns which repeats only once for eachrevolution of thespeaker housing 12. However, acceptable pulsato stillis obtained with a phase difference in the range of from about 45toabout l35this also producing an asymmetrical radiation pattern. Ofcourse, the phase difference could be an integral number of cycles plus40 to Further, either of speakers 16, 17 may lead or lag the other. Aphase difference of 0 or is not acceptable, as this would result in afigure-eight sound radiation pattern, as disclosed herein.

An alternative arrangement for providing the speaker drive signals isshown in FIG. 3. Referring thereto, the source-signal supplied via theline 22 is provided directly to a phase difference network 21'. The twospeaker drive signals produced by network 21 then are individuallyamplified by amplifiers 38, 39 and provided via the lines 35'36' to therespective speakers l6, 17.

An alternative embodiment of the inventive rotary tremolo device isshown in FIG. 4. In this embodiment, a pair of speakers 41, 42 arefixedly mounted in spaced, facing relationship in a cabinet structure43. The sound channels of the speakers 41, 42 project vertically througha respective pair of openings 44, 45 provided in the horizontalpartition walls 46, 47 interior of the cabinet 43. The speakers 41, 42respectively receive via the lines 35a, 35b a pair of drive signalsdiffering'in phase, optimally by 90as described above. i i

A rotary reflector plate or baffle 49 supported on a vertical shaft 51is used to reflect the sound from the speakers 41, 42 outwardly throughthe open front of the cabinet structure 43. The reflector plate 49 isdis posed at an acute angle, preferably 45with respect to the shaft 51.Preferably, the shaft 51 is aligned coaxially with the speakers 41, 42.Rotational motion is imparted to the reflector plate 49 by means of amotor 52, a belt 53 and a pulley 54 attached to the shaft 51.

It will be appreciated that the sound produced by the speakers 41, 42and reflected by the baffle 49 will exhibit an asymmetrical radiationpattern like that produced by the-speakers 16, 17 shown in FIGS. 1through 3. When the reflector plate 49 is rotated at between about fiveand eight revolutions per second, the asymmetrical sound radiationpattern correspondingly will rotate about a vertical axis, producing afull, rich pulsato effect.

The asymmetrical sound radiation pattern produced by the diagonallyopposed speakers 16, 17 when driven out of phase by 90 electricaldegrees is typified by the curve 60 of FIG. 5. The curve 60 is shownsuperimposed on circular coordinates centered at the speaker axis ofrotation. Although the exact shape will differ from frequency tofrequency, the radiation pattern is characterized by a region 60a ofminimum intensity in one direction and a region 60b of minimum intensityin the opposite direction. As the housing 12 isrotated about the shaft13, a listener situated at a fixed location will sense only one maximum60b for each revolution of the housing. That is, the sound radiationpattern repeats only once per revolution of the speaker support.

Intending to claim all novel, useful and unobvious features shown ordescribed,

I claim:

1. An apparatus for producing pulsato by acoustic means, comprising:

a. a support;

b. means for rotating said support about an axis;

0. first and second speakers mounted on said support on diametricallyopposite sides of said axis to be mutually counterbalanced;

d. means for supplying to the respective speakers, drive signals derivedfrom the same source signal, but differing in phase by a value otherthan either zero, 180 or a multiple of l80said drive signals producingfrom said speakers a sound radiation pattern which repeats only once perrevolution of said support.

2. The apparatus according to claim 1 in which said support is a drum,said speakers facing radially outwardly.

3. The apparatus according to claim 1 in which said rotating meansimparts rotation to said support at a rate of about five to eightrevolutions per second.

4. The apparatus according to claim 1 in which said drive signals differin phase by about 45 to 135 or by such amount plus a multiple of 180.

5. Apparatus according to claim 1 wherein .said means for drivingcomprises a phase difference network receiving said source signal andproviding said phase differing speaker drive signals.

6. Apparatus according to claim 5 further comprising means foramplifying said source signal.

7. Apparatus according to claim 5 further comprising means forseparately amplifying each of said speaker drive signals.

8. Apparatus according to claim 5 wherein said phase difference networkcomprises first and second lattice filters each receiving said sourcesignal, said source signal being substantially within the pass band ofsaid filters, said pair of speaker drive signals being providedrespectively by said first and second filters.

9. Apparatus according to claim 1 wherein said speaker drive signalsdiffer in phase by 90 or 90 plus a multiple of 180.

10. Apparatus according to claim 9 wherein said support includes agenerally cylindrical housing carried by a coaxial shaft, said speakersbeing mounted adjacent the periphery of said housing in counterbalancedrelationship.

ll. A'rotary tremolo device comprising a. a support;

b. means for rotating said support about an axis at between about flveand eight revolutions per second;

c. a pair of oppositely facing sound channels mounted in counterbalancedrelationship on said support; and

d. means for driving said sound channels with a pair of signalsdiffering in phase by an angle of between about 45 and 135or by anintegral number of cycles plus said angle, to produce from said channelsan asymmetrical sound radiation pattern which repeats only once perrevolution of said support.

12. A rotary tremolo device according to claim 9 wherein said angle is13. Apparatus for producing tremolo acoustically,

comprising:

a. first and second speakers mounted in spaced, facing relationshipalong a vertical axis;

b. planar reflecting means disposed between said speakers and mountedfor rotation about said vertical axis at a rate of between about fiveand eight revolutions per second, said planar reflecting means beingsituated at other than a right angle with respect to said vertical axis;and

0. electrical signal source means for driving said speakers with a pairof signals differing in phase by between approximately 45 and to producefrom said apparatus a sound radiation pattern which repeats only onceper revolution of said pla nar reflecting means.

14. A rotary tremolo device comprising:

a. two speakers;

b. means for driving said speakers with a pair of signals derived fromthe same source signal but differ ing in phase to produce anasymmetrical sound radiation pattern having a single major lobe; and

c. rotary means for effectively causing said asymmetrical soundradiation pattern to rotate about an axis at a slow speed, said soundradiation pattern repeating only once per revolution of said rotarymeans.

1. An apparatus for producing pulsato by acoustic means, comprising: a.a support; b. means for rotating said support about an axis; c. firstand second speakers mounted on said support on diametrically oppositesides of said axis to be mutually counterbalanced; d. means forsupplying to the respective speakers, drive signals derived from thesame source signal, but differing in phase by a value other than eitherzero, 180* or a multiple of 180said drive signals producing from saidspeakers a sound radiation pattern which repeats only once perrevolution of said support.
 2. The apparatus according to claim 1 inwhich said support is a drum, said speakers facing radially outwardly.3. The apparatus according to claim 1 in which said rotating meansimparts rotation to said support at a rate of about five to eightrevolutions per second.
 4. The apparatus according to claim 1 in whichsaid drive signals differ in phase by about 45* to 135* or by suchamount plus a multiple of 180*.
 5. Apparatus according to claim 1wherein said means for driving comprises a phase difference networkreceiving said source signal and providing said phase differing speakerdrive signals.
 6. Apparatus according to claim 5 further comprisingmeans for amplifying said source signal.
 7. ApparatuS according to claim5 further comprising means for separately amplifying each of saidspeaker drive signals.
 8. Apparatus according to claim 5 wherein saidphase difference network comprises first and second lattice filters eachreceiving said source signal, said source signal being substantiallywithin the pass band of said filters, said pair of speaker drive signalsbeing provided respectively by said first and second filters. 9.Apparatus according to claim 1 wherein said speaker drive signals differin phase by 90* or 90* plus a multiple of 180*.
 10. Apparatus accordingto claim 9 wherein said support includes a generally cylindrical housingcarried by a coaxial shaft, said speakers being mounted adjacent theperiphery of said housing in counterbalanced relationship.
 11. A rotarytremolo device comprising a. a support; b. means for rotating saidsupport about an axis at between about five and eight revolutions persecond; c. a pair of oppositely facing sound channels mounted incounterbalanced relationship on said support; and d. means for drivingsaid sound channels with a pair of signals differing in phase by anangle of between about 45* and 135or by an integral number of cyclesplus said angle, to produce from said channels an asymmetrical soundradiation pattern which repeats only once per revolution of saidsupport.
 12. A rotary tremolo device according to claim 9 wherein saidangle is 90*.
 13. Apparatus for producing tremolo acoustically,comprising: a. first and second speakers mounted in spaced, facingrelationship along a vertical axis; b. planar reflecting means disposedbetween said speakers and mounted for rotation about said vertical axisat a rate of between about five and eight revolutions per second, saidplanar reflecting means being situated at other than a right angle withrespect to said vertical axis; and c. electrical signal source means fordriving said speakers with a pair of signals differing in phase bybetween approximately 45* and 135* to produce from said apparatus asound radiation pattern which repeats only once per revolution of saidplanar reflecting means.
 14. A rotary tremolo device comprising: a. twospeakers; b. means for driving said speakers with a pair of signalsderived from the same source signal but differing in phase to produce anasymmetrical sound radiation pattern having a single major lobe; and c.rotary means for effectively causing said asymmetrical sound radiationpattern to rotate about an axis at a slow speed, said sound radiationpattern repeating only once per revolution of said rotary means.